In the hydrocarbon processing industry, many refineries recover valuable products from the heavy residual oil that remains after refining operations are completed. This recovery process is known as delayed coking Delayed coking produces valuable distillates, leaving coke as a byproduct in large vessels or coke drums. The process of delayed coking involves directing a flow of residual byproduct through an inlet from a feed source into the vessel referred to as a coke drum.
The general trend in the delayed coking industry is towards increased safety, durability, efficiency, and reliability. Utilizing a dispensing system that allows control over the dispensing, dispersion and flow patterns of residual byproducts, steam and quench fluid into a reservoir vessel may be desirable. As such, there is a need to improve how material and fluid including residual byproducts are injected into the large coke drums.
FIG. 1 illustrates one type of dispensing system. FIG. 1 illustrates a cutaway perspective view of a dispensing system attached or coupled to vessel 2, shown as a coke drum. Vessel 2 comprises a cylindrical sidewall support body 4 and a lower flange 5. Lower flange 5 further comprises a plurality of bolt holes 7 that are used to receive bolts therein to securely couple vessel 2 to another matching flanged member, such as a de-header valve or an intermediate spool assembly.
Coupled to the vessel 2 is a inlet 6, shown in the form of a cylindrical pipe having a flange segment and an opening 8 to allow inlet 6 to be in fluid connection with the interior of vessel 2. As a feedline is attached to inlet 6, the residual byproduct in the feedline may be received through opening 8 in inlet 6 and routed into vessel 2. Inlet 6 does not provide any degree of control over how the byproduct is feed into vessel 2. As a result, a significant amount of uneven heat distribution, thermal variance, and uneven flow channeling may exist within vessel 2 for which inlet 6 provides no ability to control.
FIG. 2 illustrates another type of dispensing system. Specifically, FIG. 2 illustrates a perspective view of a dispensing system attached or coupled to vessel 2, shown as a coke drum. Vessel 2 comprises a cylindrical sidewall support body 4 and a lower flange 5. Lower flange 5 further utilizes a plurality of bolt holes 7 that are used to receive high strength bolts to securely couple vessel 2 to another matching flanged member 9, such as a flanged member of a de-header valve or an intermediate spool assembly. Coupled to vessel 2 is a first byproduct dispenser, shown as inlet feed 1, and a second byproduct dispenser, shown as inlet feed 3 positioned opposite and coaxial with one another. Each of inlet feeds 1 and 3 function to dispense byproduct into vessel 2 during delayed coking.
Although the addition of another dispenser or inlet feed helps to alleviate some of the problems associated with the influx of residual byproduct into a coking vessel when a single inlet is used, the remedial effect or benefit of two opposing inlet feeds on these problems is only minimal. A significant amount of uneven heat distribution, thermal variance, and uneven flow channeling still exists within the vessel 2 because of the inability of the inlet feeds 1 and 3 to dispense byproduct in a controlled and predictable manner.
The uneven heat distribution, thermal variance, and uneven flow channeling is the result of various factors. For example, the combination of pressure within the feedline and the high temperature of the residual byproduct produce significant force within the feedline as byproduct enters an inlet. The residual byproduct may be propelled through the inlet, under pressure, into the interior of a vessel at high velocities, hitting the inner side of the vessel opposite the exit area of the inlet. While the vessel may be pre-heated, for example to a temperature of about 450° Fahrenheit, the incoming byproduct may be injected into the drum at a significantly higher temperature, for example about 900° Fahrenheit. The high velocity stream of heated residual byproduct collides with the inside surface of the sidewall support body that is perpendicular or substantially perpendicular to the direction of the flow of the fast moving, heated residual byproduct.
While the simplicity of the system depicted in FIGS. 1 and 2 may be desirable, systems that allow for additional control over the flow of heated residual byproduct into the vessel may be desirable. For example, the sudden influx of heated, pressurized material into a stagnant vessel may cause stark heat distribution variances throughout vessel 2, the sidewall support body 4, the lower flange 5, bolts connecting the vessel to other components, and other components.
For example, the heated residual byproduct may be injected into vessel 2 and impact the opposite sidewall. The impacted wall and surrounding area instantly begin to heat. This impact point on the sidewall is the thermal center from which heat is initially distributed to the other adjacent areas of vessel 2. Over time, the residual material gathers and builds up inside vessel 2 at this impact point. As this happens, the continuing influx of residual byproduct impacts the cooled, newly formed coke rather than the sidewall, altering the thermal center. As additional residual byproduct continues to be injected into vessel 2, the point of impact, and thus the thermal center, continues to move away from the opposing sidewall toward inlet 6, resulting in uneven heat distribution or thermal variance.
Uneven heat distribution, or thermal variance, existing within vessel 2 as a result of the influx of the residual byproduct in the manner described above induces uneven stress distribution within vessel 2 and the other connected components. This uneven stress can cause the vessel and the other components to wear out more quickly.
Further, because the delayed coking process typically utilizes at least two vessels in an alternating manner, this heating and cooling occurs in cycles. While one vessel is being filled the other is being purged of material and prepared to receive another batch of byproduct. During the off-cycle when a vessel is being purged of its contents, it is cooled by water and returned to a state of equilibrium. This cyclical pattern of dispensing hot residual byproduct into vessel 2 and subsequently hydroblasting the byproduct contributes to the thermal differential and stress within vessel 2. Cyclical loading and unloading or stressing and unstressing of vessel 2 is referred to as thermal cycling. In addition to other factors, thermal cycling typically results in the weakening or fatiguing of vessel 2 and its component parts, which leads to a reduction in the useful life of vessel 2.
In addition to thermal variance within the vessel and injection systems, control over the flow of heated residual byproduct into the vessel may be desirable for many other reasons. As another example, coke bed morphology may be influenced by various factors including flow channeling and quench characteristics. Flow channeling is a complex process that occurs when residual byproduct is injected into the bottom of a coke drum. For example, as the vessel begins to fill, the weight of residual byproduct pressing down may begin to influence flow-channeling patterns of residual byproduct being injected into the vessel as it is ejected from an inlet. Differing flow-channeling patterns affect the coking process.
The relationship between flow channel patterns and the coking process is complex. For example, flow channeling affects not only the introduction of residual byproduct into a coking vessel, but the introduction of steam in subsequent processes and the flow of quench fluid utilized to cool the coke bed. Even or uneven flow channeling may result in different quench characteristics.
Accordingly, the complicated process that produces a particular flow channeling pattern, such as uneven flow channeling or even flow channeling, may have an attendant effect on thermal variance in the coke drum as it is being filled. Also, the movement of steam that is injected into the coke bed to crack off volatile organic compounds may result in altered quench characteristics including but not limited to the amount of water required to cool the coke bed and the path that quench fluid follows through the coke bed during the quench cycle. For example, uneven flow channeling may result in uneven quench characteristics that may alter thermal variances in the coking vessel effectively decreasing the life span of a coke vessel.
As another example, uneven flow channeling may result in quench characteristics that cool portions of the drum and coke bed dramatically, while leaving areas of the coke bed that are not cooled sufficiently prior to being cut from the drum. Explosions of hot gas, liquid and particulate matter may occur as a cutting tool is lowered through the coke bed as the heated areas of the coke bed are encountered. These explosions can be dangerous.